sqlite storage: Do ReadAt without using incremental I/O

diff --git a/storage/sqlite/sqlite-storage.go b/storage/sqlite/sqlite-storage.go
index e4eba4beb7a2b01107a5d1dbac03b52c917160d2..2674b4d9af2a326d70d93c92b7fcce21635f6fd5 100644 (file)
--- a/storage/sqlite/sqlite-storage.go
+++ b/storage/sqlite/sqlite-storage.go
@@ -221,20 +221,48 @@ func (i instance) Stat() (ret os.FileInfo, err error) {
 
 func (i instance) ReadAt(p []byte, off int64) (n int, err error) {
        i.withConn(func(conn conn) {
-               var blob *sqlite.Blob
-               blob, err = i.openBlob(conn, false, true)
-               if err != nil {
-                       return
-               }
-               defer blob.Close()
-               if off >= blob.Size() {
-                       err = io.EOF
-                       return
-               }
-               if off+int64(len(p)) > blob.Size() {
-                       p = p[:blob.Size()-off]
+               if false {
+                       var blob *sqlite.Blob
+                       blob, err = i.openBlob(conn, false, true)
+                       if err != nil {
+                               return
+                       }
+                       defer blob.Close()
+                       if off >= blob.Size() {
+                               err = io.EOF
+                               return
+                       }
+                       if off+int64(len(p)) > blob.Size() {
+                               p = p[:blob.Size()-off]
+                       }
+                       n, err = blob.ReadAt(p, off)
+               } else {
+                       gotRow := false
+                       err = sqlitex.Exec(
+                               conn,
+                               "select substr(data, ?, ?) from blob where name=?",
+                               func(stmt *sqlite.Stmt) error {
+                                       if gotRow {
+                                               panic("found multiple matching blobs")
+                                       } else {
+                                               gotRow = true
+                                       }
+                                       n = stmt.ColumnBytes(0, p)
+                                       return nil
+                               },
+                               off+1, len(p), i.location,
+                       )
+                       if err != nil {
+                               return
+                       }
+                       if !gotRow {
+                               err = errors.New("blob not found")
+                               return
+                       }
+                       if n < len(p) {
+                               err = io.EOF
+                       }
                }
-               n, err = blob.ReadAt(p, off)
        })
        return
 }